1. Field of the Invention
The present invention relates to a liquid crystal display device, a driving control circuit to be used in the liquid crystal display device, and a method for driving the liquid crystal display device and more particularly to the liquid crystal display device having an LED (Light Emitting Diode) backlight being able to be suitably used when only moving images and moving/still images having moving images and still images in a mixed manner are displayed, to the driving control circuit, and to the method for driving the liquid crystal display device.
The present application claims priority of Japanese Patent Application No. 2006-055600 filed on Mar. 1, 2006, which is hereby incorporated by reference.
2. Description of the Related Art
In recent years, a liquid crystal display device has been used not only as a monitor of a personal computer but also as various displays such as a liquid crystal television set or a like. When the liquid crystal display device is used for such as an application to the television set or the like, performance of displaying moving images is essential. However, in the conventional liquid crystal display device, when a moving image is to be displayed, a succeeding image is displayed with a current image still persisting in a user's consciousness and, as a result, the current image is perceived by the user as an after-image. The reason for this is that much time is required for a response of a liquid crystal to an applied voltage and that a holding-type driving operation is performed in which a current frame is held till a displaying signal corresponding to a succeeding image is supplied.
The after-image caused by the response of the liquid crystal can be reduced by speeding up the response of the liquid crystal by performing an overdriving operation in which an over-voltage is applied to the liquid crystal. Also, the after-image caused by the holding-type driving operation can be reduced, as in the case of a CRT (Cathode Ray Tube) display device, by performing an impulse driving operation in which an image is displayed only for a moment. The impulse driving operation includes a method in which a black image is displayed in an inserted manner after an image is displayed on a liquid crystal display panel during one frame period (called a “black inserting driving method”) and a method in which a backlight is turned on after a specified voltage is applied in a pixel region (called a “backlight blinking method”).
Conventional technology of this type is disclosed in the following Patent Reference. In the liquid crystal display device disclosed in Patent Reference 1 (Japanese Patent Application Laid-open No. 2004-163829, page 7, FIG. 2), impulse driving operations based on the backlight blinking method are performed and, as shown in FIG. 12, after a liquid crystal comes to have specified optical transmittance with a time delay corresponding to response time of the liquid crystal following the completion of scanning for all the periods (writing of images) on a display screen, a driving waveform is applied to a backlight source. The backlight source illuminates simultaneously all the display screens at the same frequency as a frame frequency (60 Hz) during a backlight turning-on period. This enables reduction in blurring of moving images caused by a response of a liquid crystal and by a holding-type driving operation.
In the conventional liquid crystal display device disclosed in Patent Reference 2 (Japanese Patent Application Laid-open No. 2004-233932, page 6, FIG. 2), black insertion driving is performed and one frame for input data shown in FIG. 13(a) is divided into two frames in which the data input is read twice from the frame memory as shown in FIG. 13(b). Based on a controlling signal from a CPU (Central Processing Unit), a video signal or a black display signal is written on a liquid crystal display panel. In this case, as shown in FIG. 13(c), black displaying signals 1, 3, and 5 and video signals 2, 4, and 6 are written on the liquid crystal display panel. This enables suppression of blurring of moving images in the holding-type displaying.
However, the above conventional liquid crystal display device has the following problem. That is, the problem arises that, though, in the conventional technology, combination of the overdriving and impulse driving methods improves quality of moving images, a flicker occurs when the black insertion method or backlight blinking method are performed in a region having many images standing still on a display screen at a normal frame frequency (60 Hz). When an LED is used as a backlight source, a response of the LED in its turning-on to its turning-off states or vice versa is more rapid than that of a CRT and, therefore, quality of moving images by using the backlight blinking is greatly improved, however, a greater flicker occurs.
Also, another problem is that, in the conventional display device disclosed in Patent Reference 1, blurring of moving images caused by a response of a liquid crystal and caused by the holding-type driving method can be reduced, however, the backlight source flashes at the same frequency as the frame frequency and, as a result, a flicker occurs.
Moreover, in the conventional liquid crystal display device disclosed in the Patent Reference 2, a problem arises that blurring of moving images caused by the holding-type displaying can be suppressed, however, an influence of a response delay of a liquid crystal appears on a display screen and, therefore, improvement of quality of moving images can not be expected when compared with the case where the LED backlight is made to flash.